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Passenger Car Interiors via 3D Printing

By Dr. Robert Perry


    John and Connie Coy, owners of the Glacier Line, recently were going through their collection of 400 or so pieces of rolling stock.  These are 3 rail O-Scale cars, many of which have just been sitting on shelves near his fiddle yard.  Several years ago, Connie had purchased a five-car passenger set that looked great but had no interior detail and had incandescent lighting that was not working on three of the five cars.  The cars are made primarily of aluminum and had their three interior bulbs wired in series so if one burned out, none of them would light. They had always wanted to have interiors for these cars but did not relish the time that it would take to create this.  As a member of the operating crew of the Glacier Line, I suggested that they consider 3D printing the interiors as it would be much easier than fabricating them by hand.  Since they are not experienced in 3D design and printing, I offered to help.


    Now this may be sacrilege to some because the cars in question were a collector’s set of Weaver Quality Craft Models® Gold Edition 1965 O-Scale Illuminated 3 Rail Great Northern Empire Builder cars.  Since the original boxes had long since been discarded, their value as collector’s pieces was greatly reduced.  The Coys just wanted to enjoy their passenger cars and didn’t really care about the monetary value.  As such, I began designing the interiors for the five cars.


    The set comes with a baggage car, an observation car and three other cars that are somewhat nondescript.  The Weaver company had apparently made generic passenger cars that were supposed to be Pullman cars but did not have window arrangements that correlated with any known prototype.  After careful assessment it was determined which cars would be best for diner, coach and sleeper cars.


     For my 3D printing I am using a Creality®CR10S Pro V2 which is an FDM (Fused Deposition Modeling) printer as opposed to a resin printer.  I use a spare bedroom for my printing and wanted to avoid any noxious fumes generated by a resin printer.  Now I’m not an expert in CAD or 3D printing but have been gradually learning the tricks of the trade over the past five months.  I am an eye doctor but everyone else in the family are engineers.  I did teach robotics for 13 years and so, I guess, some of the tech stuff has rubbed off on me.  I am a huge advocate of learning new technologies for this hobby including electronics, Arduino programming, computer integration with JMRI® as well as CAD design with 3D printing.  In robotics, we used to use AutoDesk® Inventor but my experience with it consisted of watching over my son’s shoulders as he designed aspects of the robots.  Since Inventor is very expensive, I started using AutoDesk® Fusion 360.  This is also an expensive program but as a hobbyist you are allowed to download a version for free from AutoDesk® that is essentially full featured.  This CAD program is used professionally for both additive manufacturing (like 3D printing) as well as subtractive manufacturing (like CNC milling and lathes.)  Unlike many other programs that I have tried, this CAD program is relatively easy to learn.  There are many excellent tutorials on the AutoDesk™ website as well as in user groups and YouTube™.  It is also user-friendly in that the steps needed are common sense and you don’t forget how to use the program if you don’t use it for a while (a problem I found with many previous attempts at learning CAD.) Another common program used by hobbyists is Trimble™ SketchUp but I find Fusion 360 to be more full-featured.


  When a program is designed in one of these programs, the file (typically an .stl file) needs to be converted to a language that the 3D printer can understand (typically G-code.)  For this step I have been using either AutoDesk® Meshmixer or Ultimaker Cura® both of which are excellent and, more importantly, are free!  These programs determine how the printed parts are to be laid out on the printer, determine the toolpath (how the print nozzle goes from point to point) as well as creating any necessary supports needed during the printing process.  Supports are sometimes needed when printing overhangs as the printer needs something to lay its next layer of filament on.  It cannot print in mid-air.  An example would be the top opening of a door.  Some printers can print a dissolvable support, others, like mine print temporary supports that can be easily trimmed away later.


    The first step in producing the interiors was to disassemble the models.  This was an easy task as the end walls are screwed to the floor with two screws on each side.  Once the two ends are removed, the floor section can be slid out of the car body.  The trucks are then removed from the underside by removing one screw and sliding the truck swivel out from a slot in the underbody.  Since this is a 3-rail car, the wheels on both sides are designed to be negative power pickups.  The inner rail transfers power via a spring-loaded roller.  A small electrical connector is disconnected from the truck, thus freeing the truck and swivel entirely from the car.


     The interior of the car was not intended to be seen in the original model and utilized a semi-opaque dark green acetate that had been slid into a slot on the inside of the car body and held in place with a couple spots of hot glue.  These were easily removed, and the acetate slid out. 


     In order for the new interior to be visible, clear acetate was cut to the same size as the previous green pieces.  I needed fairly thick acetate so as to withstand any damage from someone lifting the car.  A 5 lb. clear tub of Member’s Mark™ Animal Crackers was cut into strips to make the windows.  Since passenger cars of the time period sometimes used green semi-opaque window shades, I then cut the green acetate to various window shade heights keeping it intact as one piece.  I then slid both the original green sheet as well as the new clear sheet into the same slot as the previous window glass.  This now allowed for interior viewing as well as the appearance of window shades at various levels of closure.


     The original wiring consisted of three 14V incandescent bulbs that were affixed to pieces of metal that were punched out of the underbody and bent upward creating a grounding source for the bulbs.  These tabs were bent back into the plane of the floor and hammered smooth.  Electrical tape then was used to cover any remaining opening to prevent stray light from escaping through the floor.  Being wired in series, a single wire went from one truck’s center roller to each bulb consecutively and back to the other truck.  It was decided that LED lighting with a flicker-free circuit would be used to replace the old system.  Two JW&A Item 20100 Passenger CAR LED Lighting Kits from Henning’s Trains® were ordered.  The kit consists of two LED strips, connectors and two constant power capacitor circuits.  This is enough to do two 12 to 21” cars each.  It uses far less power than the incandescents, stays flicker-free and evenly illuminates the car’s length.  It is also fully MTH® DCS compatible which was important to prevent any issues with the owners’ command control system.

     A new wire was connected to each truck’s center roller and was connected to the positive power input of the new circuit.  The other power lead was connected to the ground of the car’s frame.  A JST plug the connects the LED lighting strip to the circuit board.  This LED strip was hot-glued to the car’s ceiling.  This particular circuit comes with a small POT (potentiometer or variable resistor) that allows adjustment of the lighting level to your preference.  Since I did not want to open and close the body to adjust the lights, I left the window off of the end door of the car on the end that has the circuit.  The circuit is positioned such that a small Phillip’s screwdriver can be inserted through the window and adjust the POT to change the lighting level.  The end window being absent is not a cosmetic issue as the passenger car diaphragm obscures the view of the window anyway.


     Using a set of calipers for taking measurements of the car body and window placement, a rendering of each of the cars was produced in Fusion 360.  Using floor plans and photos of generic Pullman cars from both the internet and publications from the Great Northern Railway Historical Society a best-fit design was created to most closely match the window patterns as well as trying to keep as close to the prototype as possible. Unfortunately, the Weaver cars do not seem to be 100% to scale in regard to the height of the windows relative to the floor.  With this in mind, plans were created to either use a printed floor, carpeted floor or to glue seats and other details directly to the car’s metal floor as needed.  This was done to minimize any effect where the passengers would seem inordinately high in their seats relative to the windows.


    A Sleeper Car was designed with both bedrooms as well as roomettes.  Bathrooms were included for both the bedroom occupants as well as shared facilities for the roomette occupants.  For some slight whimsy, one of the bathrooms has a male occupant with his pants down using the commode after forgetting to fully close the door or lower the shades.


    The Dining Car was designed with a kitchen, multiple tables and a drink and pastry bar as was common on many of these cars.  The Coach Car was fairly simple as it consists of one bathroom on each end, a conductor office with desk and multiple coach chairs.  Both of these cars were carpeted using remnants from my daughter’s doll house.  The baggage car was not addressed for interior detail other than to remove the power-hungry incandescent lights.  The Pullman Lounge-Observation car was created with a lounge, shared bathroom, roomettes and sleeping compartments.


     Once I was satisfied with the design of the cars, the files were sent to the 3D printer.  Each print took between 10-15 hours.  Using a glass print bed, I merely had to wait for the bed to cool and all the items popped right off.  Walls and details were painted with era-appropriate colors.  Carpeting was glued down, and details affixed with hot glue if not already part of a one-piece printing with floor.  Seated O-Scale figures were added to the various seats, stools (and even a toilet.) The figures and lighting circuit were the only real expenses in this project.  3D printing has proven to be very inexpensive and the total cost of filament for this project totaled  approximately $10.


     Due to the small windows that were used on the Empire Builder of that generation, the interior details may seem too much for some and not enough for others. Nevertheless, the overall effect seems quite good, and the lighting is now evenly distributed, flicker-free and subdued to a realistic level.


    Creating scratchbuilt benches, tables, toilets, etc. may not be something that grabs the interest of many of us.  This is especially true when so little of the detail will ever really be seen.  It understandably did not pique interest in the Coy family into making these repetitive items.  Luckily 3D printing can relieve that tedium.  Granted there is a time commitment to creating the designs, but that is another fun aspect of the hobby.  The Coys greatly appreciate the final outcome of this task and will make the cars a frequent sight on the Glacier Line.  Hopefully this project will spur some model railroaders into doing more with 3D printing.  It is another aspect of a widely diverse skill set in this hobby that many of us are now acquiring.  

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